Click the title above to be taken to the Google Webmaster blog that explains it all.

The important take-away from the post is this…

This algorithmic change noticeably affects less than 1% of searches globally. That means that in less than one in 100 searches, a typical user might notice a reordering of results on the search page. If you believe that your website has been affected by the page layout algorithm change, consider how your web pages use the area above-the-fold and whether the content on the page is obscured or otherwise hard for users to discern quickly. You can use our Browser Size tool, among many others, to see how your website would look under different screen resolutions.